Power transmission belts for use in variable pulley transmissions comprising the general combination of interconnected links with means to engage the pulley flanges have been suggested in the art. Some of the engaging means are the ends of the interconnecting pivot means or angled sheet metal plate-like means and the like.
The use of ranks or sets of interleaved links connected to pivot means and drive blocks of generally trapezoidal shape located between adjacent drive pins to transmit load to the pins is disclosed and claimed in U.S. Pat. No. 4,313,730, issued Feb. 2, 1982 to Cole et al, entitled "Metal Chain Belt", which is assigned to the assignee of the present invention.
Other types of metal drive belts are taught, for example, by van Doorne et al in U.S. Pat. No. 3,720,113, granted Mar. 13, 1973. The belt of this patent comprises a flexible band of superimposed steel strips with metal blocks thereon having tapered edges to engage the flanges of the pulleys of a variable pulley transmission. The metal blocks in this belt move longitudinally and the load is carried by the blocks.
The projected cost of belts constructed according to van Doorne et al is several times the cost of a chain-belt as taught by Cole et al. Thus, economically, the Cole et al chain-belt is much more attractive than the van Doorne belt.
In testing a chain-belt comprising the interconnected ranks or sets of interleaved links and drive block in a pulley transmission, it has become apparent that the noise generated by the drive belt and pulley peaks at certain frequencies which are related to block-pulley flange engagement rate.
Acoustic research results have proved that a white, irregular or arhythmic noise is less noticeable and annoying than a noise which contains recognizable pure tones or a single frequency. The most annoying chain noise is the single tone or frequency which may occur above 1000 Hz. but stands above the spectrum by 5 to 10 db.